The Mannich reaction for the condensation of ammonia or a primary or secondary amine with formaldehyde and a compound containing at least one reactive hydrogen atom is well known and described, for example, in Blicke: ORGANIC REACTIONS, 1, 304-330, (1954). Application of the Mannich reaction to the preparation of aminoalkylene phosphonic acid compounds has been discussed in Fields: J. AM. CHEM. SOC., 74, 1528-1531 (1952), which discloses preparation of esters of N-substituted aminomethyl phosphonic acids by reacting an aldehyde or ketone with a mixture of a phosphite diester and a primary or secondary amine, and Frank: CHEM. REVIEWS, 61, 392-394 (August 1961) which discloses preparation of aminomethyl phosphonous acids by reaction of a mixture of hypophosphorous acid, a primary amine and a carbonyl compound which may be an aldehyde or ketone. These and other references are cited in U.S. Pat. No. 3,288,846 which teaches direct preparation of aminomethylene phosphonic acids by reaction of formaldehyde, ammonia or an amine and orthophosphorous acid. Monomeric phosphonomethylene aminomethylene carboxylate is known and has been suggested for use as a corrosion inhibitor (U.S. Pat. No. 3,483,133) and as a scale inhibitor for saline water systems (U.S. Pat. No. 3,505,238).
Although prior art products provide satisfactory results when used in water treating applications as scale inhibitors and/or corrosion inhibitors, there is now provided a new class of materials that have a unique structure. These materials are effective metal ion sequestrants and are useful in water treating applications as scale and/or corrosion inhibitors. The materials of the present invention not only are polymeric, but contain a carboxylate group as well as a phosphonate group. This combination within one molecule provides utility superior to prior art products in many applications.